A permanent International Criminal Court (ICC) to try crimes against humanity has become a reality after several more countries ratified the treaty which sets it up.

Let it be a deterrent to the wicked and a ray of hope to the innocent and helpless

UN Secretary General Kofi Annan

UN Secretary General Kofi Annan hailed the event, saying, "impunity has been dealt a decisive blow".

But many important states have failed to sign or ratify the agreement - including most Arab states, the US, China and Russia - causing some to question the court's credibility.

Although the US signed the agreement under former President Bill Clinton, the Bush administration is adamantly opposed to it because of fears its own soldiers would be unfairly prosecuted.

US fears

A group of 10 countries - including Bosnia, Cambodia, Ireland, Mongolia and Romania - signed the treaty at a ceremony at UN headquarters in New York on Thursday, bringing the total number of signatories to 66.

Out-of-bounds

The Arab-Israeli conflict

Russia and its war against separatists in Chechnya

Algeria and its conflict with Islamic rebels

At least 60 countries had to sign for the treaty to take effect.

"A page in the history of humankind is being turned," said the United Nations legal counsel Hans Corell at the ceremony.

Hundreds of people burst into applause and rose in a standing ovation as the documents were handed over.

The tribunal, which will be based at The Hague, will now come into force on 1 July, trying crimes committed after that date.

"The missing link in the international justice system is now in place," said Mr Annan.

The best defence against evil will be a court in which every country plays its part

UN Secretary General Kofi Annan

"Let it be a deterrent to the wicked and a ray of hope to the innocent and helpless," he said.

Mr Annan urged those who had not yet ratified the treaty to come on board.

"The best defence against evil will be a court in which every country plays its part," he said.

He shrugged off America's concerns that its citizens could be brought before the court over military interventions abroad.

He said the ICC would complement existing justice systems and that countries with good judiciaries, which tried their own citizens fairly would "have nothing to fear".

'Unrepresentative'

Up to now there have been only limited ad hoc tribunals to prosecute genocide, crimes against humanity and war crimes - like those established for Rwanda and the former Yugoslavia.

The ICC will be a court of last resort - trying only those cases that countries themselves cannot or will not handle.

The court will have no retrospective jurisdiction, so the hope is that it will deter future dictators, their officials and armies from committing atrocities because they know there is a forum where they can be brought to account.

The ICC will have automatic jurisdiction for crimes committed:

on the territory of a state which has ratified the treaty

by a citizen of such a state

when the Security Council refers a case to it

The BBC's diplomatic correspondent Barnaby Mason says there is a danger that the ICC will be seen as geographically unrepresentative and western dominated.

Jordan is the only Arab state party to it yet, and there are hardly any from Asia. That will matter when the judges and prosecutor are elected, probably early next year, our correspondent says.